The Wong-Sandler WS Model

Wong and Sandler (1992) have developed a mixing rule that combines an EOS with a free-energy model but produces the desired EOS behavior at both low and high densities without being density dependent, uses the existing table of parameters, allows extrapolation over wide ranges of temperature and pressure, and provides a 

The original version of the Wong-Sandler mixing rule (Wong and Sandler 1992) uses the last equality of eqn. (4.3.1) as one of the restrictions on the parameters together with the combining rule 

2206/1.7264 obtained from fitting the experimental data, and the solid lines denote the results obtained with model parameters f/j6 = A12/A21 = 2.1700/1.7264 from the DECHEMA Chemistry Series at 353 K (Gmehling and Onken 1977, Vol. 1, Pt. 1, p. 334). 

The first of these equalides results from the relation G = A -E P and that the P V term at low pressures. The second of these equalities is a result of the essential pressure independence of A at liquid densities. Therefore, the second equation for the a and b parameters comes from eqn. (4.3.3) in tlie form of 

Combining eqns. (4.3.1, 4.3.4, and 4.1.6) gives the following mixing rules  

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